The invention relates to a suspension joint and torsion spring assembly capable of working in torsion and in compression/tension and intended to be installed between two members capable of limited relative rotation about an axis of rotation and of limited relative displacement in at least one radial direction.
The assembly which is the subject of the invention is of the type which comprises an outer shell capable of being secured to one of the members, an inner shell capable of being secured to the other member, and a coupling sleeve made of elastomer, wherein the sleeve is secured with no possibility to slide to the inner and outer shells.
The invention relates more particularly, although not exclusively, to a suspension joint and torsion spring assembly for a vehicle, it being possible for one of the members to consist of a tubular crossbeam and for the other member to consist of a suspension arm.
An assembly of this type is known, for example, from German Patent No. DE-A-1,580,358. The outer shell is formed of a tube extending across the entire width of the vehicle while the inner shell consists of a tube of smaller diameter and shorter length provided on each side of the vehicle. Elastomeric coupling means arranged between the tubes are separated axially from one another for the passage of pins which anchor the inner shell of the joint to one of the members. The axial bulk of the joint, for given stiffness properties, is relatively large. Furthermore, manufacturing of such a joint is cumbersome and its structure does not allow quick and easy modifications to adapt the torsional and radial stiffness properties.
German Patent No. DE-A1-2,723,497 belonging to the same applicant describes practically the same thing and has the same drawbacks.
U.S. Pat. No. 3,121,560 describes a suspension consisting of two concentric tubes placed one inside the other and coupled one to the other by an elastomeric material, this unit being intended to constitute a suspension working in the axial direction of the two concentric tubes.
U.S. Pat. No. 3,930,550 describes a torsion bar, the movements of which are countered by a resilient system consisting of elastomer placed between two concentric tubes. This resilient system only holds against torsion and has no particular property regarding its radial resistance.
The object of the invention is, above all, to provide a suspension joint and torsion spring assembly of the above-defined type which offers great manufacturing flexibility and allows the stiffness properties to be adapted easily. It is also desirable for this assembly to make it possible, for a given torsional spring rate, to obtain a relatively small radial spring rate, particularly to improve the vibrational and acoustic comfort of a wheelset of a vehicle in contact with the ground.
According to a first embodiment of the invention, the suspension joint and torsion spring assembly comprises an outer tubular subshell, an inner tubular subshell and an intermediate coupling sleeve made of elastomer, wherein the sleeve is secured with no possibility to slide to the outer and inner subshells; said elastomeric sleeve comprising at least two cells; so that the radial spring rate of the joint is significantly reduced in at least some directions without its torsional spring rate being significantly reduced.
Each cell may extend over all or part of the circumference of the sleeve.
Said sleeve may comprise a number of cells arranged parallel to one another along the longitudinal axis of the suspension.
The cells may be arranged in pairs, symmetrically with respect to the longitudinal axis of the suspension, so as to form two arcs of a circle, the angle of which can vary between 30xc2x0 and 120xc2x0, which makes it possible to determine the amount of lessening of the radial spring rate as desired.
The cells preferably have a generally trapezoidal cross section with rounded corners, the large base being located on the outer subshell.
According to a second embodiment of the invention, the suspension joint and torsion spring assembly of the above-defined type is characterized in that it comprises at least two basic elements working in parallel, each basic element comprising an outer subshell, an inner subshell and an intermediate coupling sleeve made of elastomer, wherein the sleeve is secured with no possibility to slide to the outer and inner subshells, at least one flank of which has a concave portion on at least part of its circumference, the basic elements being arranged end to end so that the outer shell and the inner shell are formed respectively by a succession of independent and adjacent subshells, while the concave portions of the flanks form at least one cell in the elastomer by virtue of which, for a given torsional rigidity of the joint, the radial rigidity is lessened with a small axial bulk.
As a preference, a concave portion is provided on each flank of the intermediate coupling sleeve made of elastomer.
The concave portion provided on one or each flank of the coupling sleeve may extend around the entire circumference; in this case, there is no angular indexing imposed when fitting the basic element, the radial rigidity being substantially constant regardless of the polar angle.
According to another possibility, the concave portion provided on one or each flank of the coupling sleeve extends over just part of the circumference, and the successive basic elements of a suspension joint have the same angular orientation so that the concave portions are side by side as are the continuous parts of the flanks. The radial rigidity of such a joint may thus vary as a function of the polar angle of the radial direction in question.
In particular, there is a radial direction in which the radial spring rate is at a maximum, the radial spring rate being at a minimum in the direction perpendicular to the previous direction.
In general, the outer subshell and the inner subshell of each basic element is made of metal and the intermediate coupling sleeve made of elastomer is bonded on its outside and on its inside to the outer subshell and to the inner subshell, respectively.
The suspension joint and torsion spring assembly may, for example, comprise four or eight basic elements placed end to end.
The torsional spring rate may be of the order of 34 mN per degree of angle. The radial spring rate may be of the order of 4 kN/mm.
Thus, the assembly according to the invention makes it possible to obtain a significant reduction in the radial spring rate, at least in certain directions, without a significant reduction in the torsional spring rate. Inevitably, the torsional spring rate will decrease if cells are introduced, even if these are only local. However, in any event, the radial spring rate/torsional spring rate ratio becomes smaller.
Apart from the arrangements explained hereinabove, the invention consists in a certain number of other arrangements which will be discussed more fully hereinafter with regard to some exemplary embodiments which are described with reference to the appended drawings, but which are by no way restrictive.